1. Field of the Invention
The present invention relates to an electrical impedance tomographic method, in particular to a three dimensional electrical impedance tomographic method.
2. Description of the Related Art
The electrical impedance tomography (EIT) is a medical imaging technology which produces tomographic images by measuring the conductivity distribution of a certain part of human body. It is currently applied to perform photography for the internal structure of biological organization. Compared to the other conventional imaging technologies such as positron emission tomography (PET), computed tomography (CT) and magnetic resonance imaging (MRI), the EIT is a tomography technology with inexpensive price, non-invasive property and without ionizing radiation. However, the disadvantage of the EIT is that the resolution of the images produced are relatively low (when compare with CT or MRI) because it is limited by the number of electrodes which acquire the measurement data. On the other hand, having too many numbers of electrodes could reduce the signal to noise ratio of the measurement data which means poor quality of data. A general EIT image reconstruction method controls the input of a current to an object through a set of electrodes and measures the voltage values produced between the other electrodes which were not being used for inputting current into the object. Next, current is again injected into the object using a different set of electrodes, and voltage values produced between the other electrodes (which were not being used for inputting current) are measured. This is repeated until all the electrodes have been used as inputting electrodes. The measured voltages of all the measurement (this is the measurement data as discussed above) are collectively being used to reconstruct a three dimensional EIT image.
The principle of the EIT is to place the conductive electrode on the surface of the object to be imaged. Then, a small amount of alternating current is applied to some or all of the electrodes and the potential difference produced is measured by the electrodes. The data of surface electrical measurement may thus be achieved and the electrical conductivity and permittivity distribution of a part of an object to be measured may be analyzed based on the data. In the conventional technique, the U.S. Pat. No. 6,725,087 has already disclosed an element for data acquisition, processing and imaging element system connected through a communication network, and thus allowing the function of data acquisition, processing and imaging to be executed at different positions of the network. In addition, the broadband frequency of the EIT system operation ranging from 10 KHz to 10 MHz has been disclosed in the paper “A broadband high-frequency electrical impedance tomography system for breast imaging”. Although the precision of impedance measurement may be increased by increasing the frequency range of current, the resolution of the EIT system still has not been improved.
The EIT is applicable to the reconstruction the impedance distribution of an object. However, the resolution of the EIT is limited by the number and size of the electrodes. Therefore, an EIT technology with high resolution and more complete three dimensional information is urgently needed at present.